Hydrodesulfurization of crude alpha-pinene



states ate't 3,3 12,75 Patented Apr. 4, 1967 ffice This inventionrelates to the hydrodesulfurizationof crude alpha-pinene, and moreparticularly, to a process for removing sulfur compounds from crudealpha-pinene by means of a catalytic hydrogenation.

The problem of controlling and reducing water and atmospheric pollutionin the United States is becoming increasingly important. Eflluents fromsulfate (or kraft) pulp mills are major contributors to the pollutionproblem. The release of foul odors has been a major defect of the kraftpulping process ever since its development in Germany more than 70 yearsago. The odors are liberated at several points in the process which areusually widely separated in the mill, thus making the problem ofcontaining and controlling. these odors difficult.

The furnace flue gases generally contain a relatively smallconcentration of the malodorous'substances; however, the total volume ofdischarge is so great that a considerable nuisance may result.

Condensates from the multiple-effect evaporator on the black liquorrecovery system may contain a consider'able amount of the foul-smellingcompounds, thus giving rise to a secondary nuisance.

The gases liberated in relieving and blowing the digesters are a majorsource for the foul odors associated with the kraft mill. The majoroffenders-are organic sulfur compounds, the principal malodoroussubstances being hydrogen sulfide, methyl mercaptan, dimethylsulfide,and dimethyl disulfide. Control of these gases is particularly difficultbecause their rate of release is 'subject to large fluctuations inherentfrom the batch digestion process.

If the gases evolved from the digester relief valve are condensed, thematerial obtained is called crude sulfate turpentine. The crude sulfateturpentine has a foul odor due to the sulfur-compounds present.

Mass spectrometerexamination of the volatile components in thecondensate from the kraft pulp digester blow gas has confirmed thepresence of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, anddimethyl disulfide, and has shown that corresponding ethyl compounds andother sulfur-containing derivatives are not present in substantialconcentrations. Thesame sulfur compounds-have been reported present inthe-crude sulfate turpentine by Efishev, Prokhorov, and Matyushkina;also by Enkvist.

The amount of loss of volatile organic sulfur compounds associatedwiththe digester relief and blow as reported by Bergstrom and Trobeck isapproximately two pounds of sulfur per ton of pulp produced. 'Pulping ofDouglas fir produces one to five pounds of sulfur per ton of pulpproduced of the same type of organic sulfur compounds, depending uponthe pulping conditions. The most-critical factor in fixing the amount ofthis material produced is the cooking temperature. More sulfur compoundsare produced at the higher temperatures. Due to the high vapor pressureof these compounds, they readily escapeinto the atmosphere during relieffrom the digester. Some of the materials are partially condensed withthe steam and appear in the digester relief condensate (crude sulfateturpentine).

Some sulfur analyses of samples of digester relief gases by Felicetta,Peniston, and McCarthy have shown the following distribution:

His omen cunts cunts,

Sample 1 131 5, 240 7, 350 4; 095 Sample 2 138 4, 880 7, 000 3, 870

Concentrations in parts per million by volume.

Most southern kraft mills obtain some reduction in the emission ofodorous compounds from the digester gases through the recovery of thecrude sulfate turpentine. The woods used by the southern mills yield upto four gallons of crude sulfate turpentine per ton of pulp produced andmake the recovery of this material for refinement economicallyfavorable. The yield of turpentine obtained from the northern andwestern mills is somewhat lower, approximately 1;5 gallons per tonofpulp produced, and recovery for refinement is seldom practiced. The typeof trees processed, the operating conditions, and the efficiency of therecovery operation determine the yield of the turpentine obtained.

Current practices of recovery and disposal of crude sulfate turpentinefrom western pulp mills vary with different locations and with differentmills. Burning as a partial fuel requirement is practiced in some mills.Others have dumped this material into the ocean where location permits.Repeated vaporization into the atmosphere has been tried, as Well asdisposing intosettling ponds. In one case, no recovery system is usedand all relief gases and turpentine emittedfforn the digest'ers'aredis-charged into the atmosphere.

Recovery of the crude sulfate turpentine is becoming of greaterimportance as a stable market for the material has developed, and alsoas pollution restrictions are tightened. An interest'in individual pureterpene1hydro carbons has also developed in the last few years and newsources of the basic terpenes are being sought. p

Once the crude sulfate turpentine has been recovered; the problem thenbecomes that of desulfurization'and purification to provide a productthat will meet withpublic acceptance and also have the same desirablechemical and physical properties associated with pure gum spirits ofturpentine. Many methods have been employed to accomplish these taskswith steam distillation and/or chemical treatment. Treatingwithhypo'chlorite or ethylene-diamine to further reduce the sulfurcontent appear to be the most common. Accordingly, this invention has asan object the provision of an improved hydrogenation' process which willselectively convert the sulfur compounds in the crudev alpha-pinene tohydrogen sulfide while not appreciably alfecting'the unsaturatedcharacter of the alpha-pinene.

A further object of this invention is to provide a catalyst which willcarry out the selective hydrogenation of the crude alpha-pinene withoutitselfbeingappreciably destroyed or inactivated.

These objects are accomplished by the present invention wherein thecrude alpha-pinene and gaseous hydrogen are passed over acobalt-molybdate catalyst.

More specifically, the hydrogenation conditions include a temperaturerange of 300 F. to 500 F., pressures from 0 to 500 pounds per squareinch, liquidjh'ourly space velocities of 1;25to 20 hour andhydrogen'rates of 1000 to 20,000 standard cubic feet per 42-gallonbarrel of liquid feed.

The process is characterized by liquid yields in excess of percent andthe effluent liquid will contain 20 percent or less of its originalsulfur content. The preferred catalyst consists of A" to pellets ofalumina containing approximately 3% cobalt oxide and 15% molybdenum'oxide. 3 a

The activity of catalyst is enhanced by pre-sulfiding. This isaccomplished by passing a gaseous mixture containing 80 volume percenthydrogen, 20 volume percent hydrogen sulfide over the catalyst at 400F.for about three hours.

The catalyst is rugged in this reaction. If it is used in the range ofconditions designat'ed,it will operate for at least 600 volumes of oilper volume of catalyst with no deactivation.

The following examples illustrate the remarkable results obtained inaccordance with our invention on crude alpha-pinene obtained from widelyscattered sources: 1 Example 1.-A feed comprising the alpha-pinenefraction from crude sulfate pulp liquor obtained from Springfield,Oregon, was passed over a catalyst comprising /8 pellets of HoudrySeries C cobalt molybdate. ,This feed contained 510 p.p.m. of sulfur.Operating conditions comprised pressure, 25 p.s.i.g.; hydrogen rate,5000 s.c.f./bbl.; temperature, 400 F.; liquid space velocity, 2.5 hour-The liquid yield was 95+% and the effluent liquid product contained 55p.p.m. of sulfur.

Under identical operating conditions and the same catalyst, crudealpha-pinches from the following sources and sulfur content were treatedand yielded the following final sulfur content.

, Example 2.-The crude alpha-pinene fraction from Springfield, Oregon,sulfate pulp mill liquor was passed over cobalt molybdate catalyst inthe presence of hydrogen under the following conditions: pressure, 25p.s.i.g.; temperature, 500 F.; hydrogen rate, 5000 s.c.f./bbl.; liquidspace velocity, 10 hour- The sulfur content of the feed was 510 p.p.m.;the product contained 140 p.p.m. The yieldof liquid product exceeded96%. Example 3.-The crude'alpha-pinene fraction from Springfield,Oregon, sulfate pulp mill liquor was passed over cobalt molybdatecatalyst in the presence of hydrogen under the following conditions:pressure, 25 p.s.i.g.; temperature, 450 F.; hydrogen rate, 5000s.c.f./bbl.; liquid space'velocity, hour ment, the sulfur content of thefeed was reduced from 510 p.p.m. to 95 p.p.m. The yield of liquid was97%. Example 4.-The following table shows the effect of space velocityon sulfur removal using the cobalt molybdate catalyst:

As a result of this treat-' reactor pressure on sulfur removal using thecobalt moly-bdate catalyst: V

Sulfur Content of Product, p.p.m. Average Reactor Pressure ConversionTrial 1 Trial 2 Average 70 75 72. 5 v 85.8 105 95 100.0 80.5 125 105115.0 77. 5 145 135 140. 0 72. 6 500 42% pinane These data indicate'thatincreased pressure reduces somewhat the amount of desulfurization. The500 p.s.i.g. run gave a 42% of pinane indicating that at this pressure,hydrogen adds, across the double bond in the alphapinene to drasticallyreduce the yield of the alpha-pinene. Example 6.The following'ta-bleshows the'eifect of temperature on sulfur removal using the cobaltmolybdate catalyst: Feedstock: Crude alpha-pinene from Springfield,Oregon sulfate pulp mill liquor. Sulfur Content of Feedstock: 510 p.p.m.

' Reactor Pressure: 25 p.s.i.g

Feedstock: Crude alpha-pinene from Springfield, Oregon sulfate pulp r.vSulfur Content of Feedstockf 510 p.p.m.

Reactor Temperature: 40 Reactor Pressure: 25 p.s.i.g. Hydrogen Rate:5000 s.c.f./bbl.

These data show that when other conditions are held constant, the lowerthe space velocity, the greater is the desulfurization.

Example 5.-The following table shows the effect of Hydrogen Rate: 5000s.c.f./bbl.

, Sulfur Content of Average Space Product, p.p.m. Conver- Reactor Temp.,F. Velocity sion,

hr.- Percent Trial 1' Trial 2 These data show the greatestdesulfurization is obtained is about 400 F. and a liquid space velocityof 2.5 hrr Example 7.-The following table shows the effect of hydrogenrate'on sulfur removal using the cobalt molybdate catalyst:

mill liquor. Sulfur Content of Feedstock: 510 p.p.m. ReactorTemperature: 40 F. Reactor Pressure: 250 p.s.i.g. Liquid Space Velocity:5 hour- Feedstock: Crude alpharpinene from Springfield, Oregon sulfatepulp Hydrogen Rate, Sulfur Content of Percent Conversion s.c.f./bbl.Product, p.p.m.

These data show that approximately 5000 s.c.f./bbl. of

hydrogen are required to obtain good desulfurization and that rateshigher than this give little benefit.

The examples presented above show the effect of the variablestemperature, pressure, space velocity, and hydrogen rate on thedesulfurization of crude alpha-pinene. We have shown that by propercontrol of these variables, 60 to 90 percent sulfur removal can beaccomplished with the cobalt molybdate catalyst.

Our invention has great economic advantages. The crude alpha-pinenecontaining 150 p.p.m. or more of sulfur is a malodorous liquid havinglittle economic use other than a cheap fuel. After treatment by ourprocess,

liquid, useful as a paint thinner, solvent, and raw mate rial forfurther syntheses.

1. A method for reducing the amount of sulfur compounds in thealpha-pinene fraction of sulfate pulp mill liquor which comprisespassing said fraction over a cobalt molybdate catalyst at temperaturesin the range of 300 F. to 500 F., pressures from 0 to 500 pounds persquare inch gage, liquid hourly space velocities in the range of 1.25 to20 hourand hydrogen rates in the range of 1000 to 20,000 standard cubicfeet per 42-gallon barrel of liquor feed.

2. A method as defined in claim 1 in which the temperature is maintainedat about 400 F. and the pressure at about 25 p.s.i.g.

References Cited by the Examiner UNITED STATES PATENTS DELBERT E. GANTZ,Primary Examiner. C. R. DAVIS. Assistant Examiner.

1. A METHOD FOR REDUCING THE AMOUNT OF SULFUR COMPOUNDS IN THEALPHA-PINENE FRACTION OF SULFATE PULP MILL LIQUOR WHICH COMPRISESPASSING SAID FRACTION OVER A COBALT MOLYBDATE CATALYST AT TEMPERATURE INTHE RANGE OF 300*F. TO 500*F., PRESSURES FROM 0 TO 500 POUNDS PER SQUAREINCH GAGE, LIQUID HOURLY SPACE VELOCITIES IN THE RANGE OF 1.25 TO 20HOUR-1, AND HYDROGEN RATES IN THE RANGE OF 1000 TO 20,000 STANDARD CUBICFEET PER 42-GALLON BARREL OF LIQUOR FEED.